Volume 9, Number 2, 2008
© Mary Ann Liebert, Inc.
Local Anesthetics as Antimicrobial Agents: A Review
SVENA M. JOHNSON, BARBARA E. SAINT JOHN, and ALAN P. DINE
Background: Since the introduction of cocaine in 1884, local anesthetics have been used as a
mainstay of pain management. However, numerous studies over the past several decades have
elucidated the supplemental role of local anesthetics as antimicrobial agents. In addition to
their anesthetic properties, medications such as bupivacaine and lidocaine have been shown
to exhibit bacteriostatic, bactericidal, fungistatic, and fungicidal properties against a wide
spectrum of microorganisms.
Methods: A comprehensive literature search was conducted using MEDLINE 1950—present
for in vitro and in vivo studies pertaining to the antimicrobial activity of various local anes-
thetics on a broad range of bacterial and fungal pathogens. Studies testing the effect on mi-
crobial growth inhibition of local anesthetics alone and in combination with other agents,
such as preservatives and other medications, as well as the effect of conditions such as con-
centration and temperature, were included for review. Outcome measures included colony
counts, area-under-the-curve and time-kill curve calculations, minimum inhibitory concen-
trations, and post-antibiotic effect.
Results: Evidence suggests that local anesthetics as a class possess inherent antimicrobial
properties against a wide spectrum of human pathogens. Multiple local anesthetics at con-
centrations typically used in the clinical setting (e.g., bupivacaine 0.125%–0.75%; lidocaine
1%–3%) inhibit the growth of numerous bacteria and fungi under various conditions. Dif-
ferent local anesthetics showed various degrees of antimicrobial capacity; bupivacaine and li-
docaine, for example, inhibit growth to a significantly greater extent than does ropivacaine.
Greater concentrations, longer exposure, and higher temperature each correlate with a pro-
portional increase in microbial growth inhibition. Addition of other agents to the anesthetic
solutions, such as preservatives, opioids, or intravenous anesthetics such as propofol, mod-
ify the antimicrobial activity via either synergistic or antagonistic action. Limited studies at-
tribute the mechanism of action of antimicrobial activity of local anesthetics to a disruption
of microbial cell membrane permeability, leading to leakage of cellular components and sub-
sequent cell lysis.
Conclusions: Local anesthetics not only serve as agents for pain control, but possess an-
timicrobial activity as well. In such a capacity, local anesthetics can be considered as an ad-
junct to traditional antimicrobial use in the clinical or laboratory setting. Additionally, cau-
tion should be exercised when administering local anesthetics prior to diagnostic procedures
in which culture specimens are to be obtained, as the antimicrobial activity of the local anes-
thetic could lead to false-negative results or suboptimal culture yields.
I-Flow Corporation, Lake Forest, California.
JOHNSON ET AL.
such as anesthetic regimens, antimicrobial use,
and perioperative fluid management. The con-
nection between the relief of pain and infec-
tions of surgical incisions remains unclear. Un-
relieved pain increases vasoconstriction in the
periphery, leading to a reduction of perfusion
and oxygenation of the tissue surrounding the
incision. This decrease in tissue oxygenation
may increase the risk of surgical site infections.
Tissue perfusion delivers oxygen, inflamma-
tory cells, growth factors, cytokines, and nutri-
tional components to injured tissues. Hypo-
perfused regions become hypoxic, with tissue
oxygen tensions that do not support adequate
oxidative killing or scar formation. In a hypoxic
environment, wound healing is arrested by de-
creased fibroblast proliferation, collagen pro-
duction, and capillary angiogenesis. Hypoxia
also facilitates growth of anaerobic organisms,
further complicating wound healing and in-
creasing the risk of infection. A significant in-
crease in tissue oxygenation of the hypoper-
fused infected wound influences the rate of
collagen deposition, angiogenesis, and bacter-
ial clearance in wounds .
In response to tissue trauma, neutrophils,
lymphocytes, macrophages, and fibroblasts mi-
grate to the site of injury . Hypoxia, which
is present to some degree in all wounds, im-
pairs the function of these cells. These con-
ditions may interfere with host defenses and
collagen deposition, particularly fibroblast
function. Many studies, both in vitro and in
vivo, show that collagen deposition is propor-
tional to the partial pressure of oxygen over the
range observed in wounds and that the rate of
surgical site infection is linked closely to oxy-
gen tension [3,4]. Furthermore, in vitro studies
by Hohn et al.  and Mandell  demon-
strated that hypoxia suppresses the killing of
Staphylococcus aureus by wound leukocytes.
Consequently, higher infection rates in surgi-
cal incisions may result from the impaired
killing of bacterial contaminants by leukocytes
in hypoxic or ischemic tissue. The combination
of decreased vascular supply and increased cel-
lularity results in a hypoxic environment
within the incision.
The role of local anesthetics in local tissue
ANY FACTORS INFLUENCE THE DEVELOPMENT
of postoperative surgical site infections,
oxygenation and perfusion is in part attribut-
able to the inherent vasodilatory properties of
the agents . One of the properties of local
anesthetics that determines their level of anal-
gesic activity is their effect on blood vessels in
areas where they are injected. Local anesthet-
ics, with the exception of cocaine and ropiva-
caine, cause peripheral vasodilation by direct
relaxation of vascular smooth muscle, which
serves not only to enhance vascular absorption
of the local anesthetic, but also to ensure de-
livery of oxygen and other nutritional compo-
nents to the tissues. The blood concentrations,
duration of action, and the proportion of ves-
sel dilation associated with each agent modu-
late the systemic effects.
LOCAL ANESTHETICS AS
ANTIMICROBIAL AGENTS: A REVIEW
The results of a multitude of in vitro and in
vivo studies over the past several decades have
substantiated a supplemental role of local anes-
thetics in the potential prevention and treat-
ment of surgical site infections. In 1976, James
et al.  examined the effect of bupivacaine on
bacterial growth, in addition to the incidence
of contamination of catheters and syringes
used during epidural analgesia. Syringes in
5/101 cases were found to be contaminated
with skin commensal organisms (i.e., Staphylo-
coccus epidermidis), likely originating from the
personnel administering the epidurals; catheter
tips were not contaminated. In this study, bupi-
vacaine (0.25%) proved bactericidal to both S.
epidermidis and Corynebacterium spp. at 37°C,
but not at room temperature (Table 1).
Further evidence of the antimicrobial effect
of local anesthetics was presented by Rosen-
berg et al. . Those authors reported that high
clinical concentrations (? 0.25%) of the local
anesthetic bupivacaine inhibited the growth of
multiple bacterial and fungal organisms,
namely Escherichia coli, S. aureus, S. epidermidis,
Streptococcus pneumoniae, S. pyogenes, Enterococ-
cus faecalis, Bacillus cereus, and Candida albicans.
With an agar dilution method, bupivacaine
was found to have antimicrobial activity
against nine of the ten microbial strains tested,
suggesting a protective effect against bacterial
INHIBITORY PROPERTIES OF LOCAL ANESTHETICS FOR VARIOUS BACTERIA
8–18, 20, 30
B. cereus, Candida spp.,
MSSA, Micrococcus spp.,
Bacillus spp., B. subtilis,
11, 13, 16,
B. catarrhalis, B. cepacia,
28, 34, 37,
A. niger, B. subtilis,
21, 27, 3
A. niger, B. subtilis
A. niger, B. subtilis
A. niger, B. subtilis
A. niger, B. subtilis
MRSA ? methicillin resistant Staphylococcus aureus; MSSA ? methicillin susceptible S. aureus.
JOHNSON ET AL.
and fungal infections; only Pseudomonas aerug-
inosa showed no inhibition of growth at bupi-
vacaine concentrations as high as 5 mg/mL
(0.5%). Morphine 0.2 and 2 mg/mL failed to in-
hibit the growth of any of the ten strains.
Hodson et al.  compared the antibacter-
ial activity of the isomers bupivacaine and
levobupivacaine against S. epidermidis, S. au-
reus, and E. faecalis, and found the minimum
bactericidal concentration of bupivacaine to be
lower than that of levobupivacaine (0.25% vs.
0.5%, respectively). Racemic bupivacaine there-
fore appears to have more potent antimicrobial
activity than its isomer levobupivacaine.
Noda et al.  performed quantitative
analysis of the antibacterial activity of local
anesthetics by calculating their minimum in-
hibitory concentration (MIC), killing curves,
and post-antibiotic effect (PAE). Colonies of S.
aureus, S. epidermidis, and P. aeruginosa were
used in the study. At standard clinical concen-
trations, both bupivacaine and lidocaine had
bactericidal activity against the aforemen-
tioned species. A comparison of MIC values
indicated that bupivacaine has greater antibac-
terial activity than lidocaine. At equal concen-
trations, even greater antibacterial activity was
found when preservatives were added to the
anesthetics, as is common in commercial solu-
tions. The preservatives alone, however, were
only weakly bacteriostatic and not bactericidal,
merely enhancing the bactericidal activity of
the pure anesthetic solutions. Similarly, Grim-
mond and Brownridge  showed increasing
microbial inhibition with increasing concentra-
tions of bupivacaine and pethidine (meperi-
dine) using an agar dilution method. At clini-
cal concentrations, bupivacaine inhibited eight
of ten pathogens tested, and pethidine inhib-
ited six, confirming the antimicrobial potential
of local anesthetics.
In addition to examining the antimicrobial
capacity of particular
Sakuragi et al.  analyzed the rate of onset
of bacterial growth inhibition. Bupivacaine
(0.125%, 0.25%, and 0.5%), mepivacaine (2.0%),
lidocaine (2.0%), and lidocaine (2.0%) with
preservatives were each tested with two strains
of methicillin-resistant S. aureus (MRSA) for 1,
3, 6, 12, and 24 h at room temperature and
cultured subsequently on agar. The authors
found that the greater the exposure time, the
greater the growth inhibition, corresponding to
lower colony counts. Bupivacaine (0.5%)
showed the greatest antimicrobial activity,
likely bactericidal, inhibiting growth by more
than 99% at 24 h, 70% at 6 h, and 60% at 3 h.
Colony counts were highest using 0.125% bupi-
vacaine and 2.0% mepivacaine.
In a follow-up study, Sakuragi et al.  ex-
amined the bactericidal activity of preserva-
tive-free bupivacaine (0.125%, 0.25%, 0.5%, and
0.75%) for two strains of MRSA, two strains of
methicillin-susceptible S. aureus (MSSA), S. epi-
dermidis, and E. coli. The pathogens were ex-
posed to the bupivacaine for 1, 3, 6, 12, and 24
h at 37°C and room temperature. The results
showed both temperature- and concentration-
dependent bactericidal activity. Increasing con-
centrations of bupivacaine correlated with
lower colony counts. Likewise, increasing tem-
peratures from room temperature to 37°C in-
creased the growth inhibition of the S. aureus
strains from 81% to 96% at 24 h with 0.5% bupi-
vacaine, and 22% to 34% at 1 h. No E. coli or S.
epidermidis growth occurred at all after 24 h at
37°C; in fact, E. coli growth was inhibited at 12
h. Thus, S. epidermidis and E. coli proved more
sensitive than S. aureus to the bactericidal ac-
tivity of bupivacaine.
In an earlier complementary study in 1997,
Sakuragi et al.  used the same parameters,
yet examined the antimicrobial effect of preser-
vatives (methyl para-oxybenzoate and propyl
para-aminobenzoate) alone and when added to
0.5% bupivacaine. Preservatives alone showed
significantly lower bactericidal activity than
when combined with bupivacaine. As in the
previous study, increasing the temperature
from room temperature to body temperature
increased the growth inhibition of S. aureus
from 89.6% to 99.8% at 12 h and from 24% to
74% at 1 h using 0.5% bupivacaine with preser-
vatives. Again, S. aureus was found to be more
resistant to the bactericidal activity of bupiva-
caine than S. epidermidis and E. coli.
Aydin et al.  examined the antimicrobial
activity of the local anesthetics ropivacaine,
bupivacaine, lidocaine, and prilocaine on vari-
ous pathogens, namely E. coli, S. aureus, P.
aeruginosa, and C. albicans. Of the four drugs
tested, lidocaine and prilocaine had the most
potent antimicrobial activity, both inhibiting all
growth of all pathogens tested at anesthetic
ANTIMICROBIAL LOCAL ANESTHETICS
concentrations of 2%; at a concentration of 1%,
prilocaine inhibited the growth of E. coli, S. au-
reus, and P. aeruginosa, whereas 1% lidocaine
inhibited only P. aeruginosa. Bupivacaine was
found to inhibit only P. aeruginosa at ? 0.25%
concentrations, whereas ropivacaine failed to
inhibit the growth of any pathogens. Pere et al.
 also found ropivacaine to have less an-
tibacterial effect than bupivacaine, as did Ro-
drigues et al. , who conducted a study using
C. albicans. In the case of C. albicans, Rodrigues
et al. suggested that the local anesthetics in-
hibited fungal germ tube formation secondary
to a blockade of ionic channels. Batai et al. 
found that ropivacaine 2 mg/mL supported
the growth of E. coli, whereas a higher concen-
tration (10 mg/mL) killed both E. coli and S.
Pina-Vaz et al.  evaluated the antifungal
activity of benzydamine, lidocaine, and bupi-
vacaine against 20 Candida strains, including
C. albicans. The activity of the three drugs was
analyzed by viability counts under epifluo-
rescence microscopy. The antifungal activity
progressed from fungistatic at lower concen-
trations, secondary to yeast metabolic impair-
ment, to fungicidal at higher concentrations,
secondary to cytoplasmic membrane damage,
as evidenced by staining.
Sporicial activity of local anesthetics and
their preservatives was tested by Abdelaziz
and el-Nakeeb . The local anesthetics pro-
caine, lignocaine (lidocaine), amylocaine, cin-
cochaine, and amethocaine, all at a 1% concen-
tration, as well as the preservatives cetrimide,
chlorocresol, chlorhexidine, phenoxyethanol,
and phenylmercuric nitrate were tested alone
and in binary combinations to assess their ef-
fects on the growth of Bacillus subtilis and As-
pergillus niger spores at various temperatures.
Inhibition of growth proved to be temperature-
dependent for all agents. Amethocaine was
sporicidal (99% death) against A. niger at the
lowest temperature (30°C), followed by amy-
locaine and cincochaine (45°C), lignocaine
(48°C), and procaine (50°C), compared with
58°C for the saline control. Higher tempera-
tures were required to elicit sporicidal activity
against B. subtilis. Cincochaine proved sporici-
dal at the lowest temperature (60°C), followed
by amylocaine and amethocaine (84°C and
90°C, respectively). Procaine, lignocaine, and
the saline control required temperatures ?
100°C to kill 99% of the B. subtilis spores.
Among the preservatives, chlorocresol/local
anesthetic combinations exhibited the highest
INTERACTIONS OF LOCAL
ANESTHETICS WITH PROPOFOL
Propofol, an agent commonly used during
operative anesthesia in an emulsion formula-
tion, promotes the rapid growth of microor-
ganisms and has been implicated as a source of
postoperative sepsis and surgical site infection.
Local anesthetics, particularly lidocaine, often
are added to the solution to minimize pain on
intravenous injection. Several authors have in-
vestigated whether this addition of local anes-
thetic confers microbial growth inhibition.
Gajrag et al.  examined the antimicrobial ef-
fect of lidocaine in the presence of propofol on
cultures of E. coli and other pathogens. The in-
vestigators found that lidocaine–propofol mix-
tures inhibited bacterial growth significantly,
whereas propofol alone increased the growth
rate. Increasing concentrations of lidocaine led
to a proportional increase of bacterial growth
inhibition. Such results suggest that lidocaine
may help to prevent surgical infection even in
cases where extrinsic propofol contamination
has occurred. Likewise, Sakuragi et al. 
found colony counts of E. coli to be significantly
lower after exposure to either lidocaine (1%,
2%, or 4%) or lidocaine (0.25%-4%)–propofol
mixtures, leading to the conclusion that lido-
caine confers bacteriostatic activity when
added to extrinsically contaminated solutions
Wachowski et al.  arrived at the opposite
conclusion. Those authors used parameters
similar to those in the previous studies, com-
paring the growth of four microorganisms (E.
coli, P. aeruginosa, S. aureus, and C. albicans)
in solutions of propofol, lidocaine, and propo-
fol ? lidocaine at 20°C. However, the concen-
trations of lidocaine used in this study were
considerably lower than those tested by
Sakuragi et al. . Wachowski et al.  found
that the addition of 0.2% and 0.5% lidocaine to
propofol failed to inhibit the growth of the
JOHNSON ET AL.
aforementioned pathogens and concluded that
clinically relevant concentrations of lidocaine
did not exhibit antimicrobial properties when
added to contaminated propofol. In a letter to
the editor, Driver  described such a claim
as misleading. Driver argued that the condi-
tions maintained in Wachowski’s study, such
as temperature, pH, and drug concentration,
were either suboptimal or unspecified. In their
own study, Driver et al.  did in fact achieve
results that supported bacterial growth inhibi-
tion using a mixture of propofol/lidocaine.
Aliquots of S. aureus diluted to a 1:108ratio
were incubated at 37°C and transferred to so-
lutions containing either lidocaine, propofol, or
a mixture of the two. Colony counts were low-
est in the mixture and highest in the propofol
solution alone. Such results suggest a syner-
gistic antimicrobial action achieved with the
combination of lidocaine and propofol that ex-
ceeds that of either of the two agents alone. Dri-
ver proposed activation of the lidocaine driven
by the higher pH when the two agents are com-
Another local anesthetic, lignocaine, was
tested by Ozer et al.  to assess its effect on
bacterial growth in contaminated propofol
emulsions. Cultures of E. coli, S. aureus, S. epi-
dermidis, and P. aeruginosa were incubated at
37°C and added to either propofol alone or a
propofol/lignocaine mixture (0.1%–2.0%). A
significant decrease in colony-forming units
(CFU) numbers was seen with E. coli in mix-
tures of 1% and 2% lignocaine. With the three
other pathogens, only 2% lignocaine signifi-
cantly suppressed colony counts. As the rec-
ommended clinical doses of lignocaine are
reported to be 0.05%–0.1%, the authors con-
cluded that this particular local anesthetic ex-
hibits inadequate antimicrobial activity to pre-
vent infection in a clinical setting.
The addition of other agents, namely opioids,
to local anesthetic solutions was tested by in-
vestigators including Feldman et al. . Vari-
ous bacteria were cultured in agar media
preparations containing clinical concentrations
of lidocaine, bupivacaine, fentanyl, or sufen-
tanil and in mixtures of bupivacaine with each
of the two opioids. Reinforcing the findings of
Rosenberg et al. , both lidocaine and bupi-
vacaine were found to inhibit bacterial growth
significantly, whereas the opioids failed to in-
hibit growth. The degree of growth inhibition
was directly proportional to the concentration
of local anesthetic; decreasing concentrations of
the local anesthetic yielded a significant re-
duction in bacterial growth inhibition, particu-
larly for certain species such as S. aureus.
In 2003, Kampe et al.  studied the effect
of ropivacaine (0.1%) when mixed with sufen-
tanil (1 mcg/mL) on the growth of the
pathogens S. aureus and P. aeruginosa at room
temperature. The combination of the local anes-
thetic and the opioid inhibited growth of P.
aeruginosa significantly; multiplication of S. au-
reus was slowed as well.
Tamanai-Shacoori et al.  extended pre-
vious study to the local anesthetics ropiva-
caine and bupivacaine in 2004. The effect of
ropivacaine (1.2 mg/mL), bupivacaine (0.77
mg/mL), sufentanil (0.38 and 0.5 mcg/mL),
and combinations of sufentanil and the two lo-
cal anesthetics on the growth of E. coli, S. au-
reus, and E. faecalis at 37°C was investigated.
Both bupivacaine and ropivacaine alone were
found to inhibit growth of E. coli and S. aureus,
yet both were ineffective against E. faecalis. The
addition of sufentanil to each of the two local
anesthetics had opposing effects, modifying
the antimicrobial activity of each drug. When
combined with bupivacaine, sufentanil exhib-
ited a synergistic effect, increasing the
inhibitory effect on the growth of all three
pathogens. When added to ropivacaine, how-
ever, the antibacterial activity of the mixture
was lower than that of ropivacaine alone,
thereby exerting an antagonistic effect.
EFFECTS OF LOCAL ANESTHETICS ON
THE YIELD OF BACTERIAL CULTURES
Because of this antimicrobial activity, several
studies have focused on the potential of local
anesthetics to interfere with clinical diagnostic
cultures and lead to false-negative results. With
the sensitivity of bronchoalveolar fluid (BAL)
cultures as low as 50%–60% for the diagnosis
of pneumonia, Anding et al.  investigated
the antimicrobial activity of local anesthetics
used in the procedure as a possible explanation
for the low sensitivity found with bronchos-
ANTIMICROBIAL LOCAL ANESTHETICS
copy. The bactericidal potential of various con-
centrations (0.01%–1%) of the local anesthetic
oxybuprocaine was tested against 104/mL
inocula of S. pneumoniae, Haemophilus influen-
zae, P. aeruginosa, and E. coli. Time–kill curves
against S. pneumoniae and H. influenzae with
even the lowest concentration of oxybupro-
caine (0.01%). Oxybuprocaine 1% inhibited the
growth of E. coli and P. aeruginosa. If local anes-
thetics such as oxybuprocaine are used prior to
obtaining material for culture, false-negative
results may ensue.
Olsen et al.  investigated the effect of
adding lidocaine to suspensions of BAL fluid
contaminated with clinical respiratory isolates.
There was significant inhibition of the growth
of two of the four S. pneumoniae isolates in the
presence of lidocaine compared with saline
controls, suggesting that S. pneumoniae may be
underestimated as a pathogen with the use of
the local anesthetic lidocaine.
A recent study in 2005 by Chandan et al. 
examined whether lignocaine (1% and 2%), an-
other anesthetic agent commonly used prior to
bronchoscopy and BAL procedures, inhibited
growth of respiratory tract flora, particularly S.
pneumoniae, Moraxella catarrhalis, H. influenzae,
P. aeruginosa, and C. albicans. With a microbroth
dilution method, lignocaine 2% exhibited bac-
tericidal activity against S. pneumoniae, M. ca-
tarrhalis, and H. influenzae; however, no inhibi-
tion of growth of P. aeruginosa or C. albicans was
observed. Lignocaine 1% partially inhibited the
growth of S. pneumoniae. Because of such an-
timicrobial activity, the authors advise using
the lowest concentration possible of local anes-
thetic prior to bronchoscopy and BAL proce-
dures in order to maximize recovery of
pathogens on culture.
Aldous et al.  also investigated the po-
tential for false-negative results with culture
specimens when using local anesthetics. The
antimicrobial activity of 4% lidocaine with
phenylephrine and 4% cocaine in nasal pro-
cedures was examined. Both agents exhibited
antimicrobial activity against the following
pathogens: S. aureus, S. pneumoniae, K. pneumo-
niae, H. influenzae, M. catarrhalis, and Enterobac-
ter spp., with cocaine exhibiting greater inhibi-
tion than lidocaine. The authors recommended
using a low concentration of anesthetic to de-
crease the possibility of obtaining false-nega-
Topical anesthetics are used routinely prior
to obtaining bacterial cultures for ophthalmic
diagnoses such as bacterial keratitis as well.
Mullin and Rubinsfeld  examined the bac-
teriostatic and bactericidal effects of three pre-
served anesthetic agents, proparacaine, tetra-
caine, and cocaine, on P. aeruginosa and S.
aureus. Proparacaine exhibited the strongest an-
timicrobial activity, inhibiting the growth of S.
aureus at even the lowest concentration of
0.125%, whereas P. aeruginosa was inhibited at
0.25% and 0.5%. Tetracaine inhibited growth of
S. aureus at 0.5% and P. aeruginosa at 0.25% and
0.5% concentrations. Cocaine exhibited only
mild inhibition of growth of P. aeruginosa at a
4% concentration. Because culture yields are re-
portedly suboptimal in diagnosing clinical ul-
cerative keratitis, the authors proposed that this
growth inhibition by local anesthetics is a likely
reason, and recommended that clinicians use a
low concentration of the minimally inhibitory
cocaine in place of the standard commercial
anesthetics in order to optimize culture yields.
OF ACTION OF LOCAL ANESTHETICS
An early study by Leung and Rawal in 1977
 reported on a mechanism of action by
which tetracaine exerts its bactericidal action
on the bacterial cell. The authors found that
tetracaine damaged the cell membrane of P.
aeruginosa through lysis, leakage of intracellu-
lar components, dehydrogenase activity, and
increased cell wall permeability.
OF SURGICAL SITE INFECTION
Parr et al.  analyzed the antibacterial ac-
tivity of clinical doses of lidocaine with and
without epinephrine on isolates of a spectrum
of bacterial pathogens common in surgical site
infections, namely E. faecalis, E. coli, P. aerugi-
nosa, S. aureus, MRSA, and vancomycin-resis-
JOHNSON ET AL.
tant enterococci (VRE). Addition of epinephrine
to the local anesthetic solution decreased the
rate of vascular absorption, thereby improving
the depth and prolonging the duration of local
action. Lidocaine inhibited the growth of all
pathogens tested independent of the presence
or absence of epinephrine in a dose-dependent
fashion. The local anesthetic had the greatest ef-
fect on E. coli and P. aeruginosa, the gram-nega-
tive organisms, and the least effect on S. aureus.
Given the results of this study, the authors made
the assertion that “wider application of the use
of local anesthetics should be mandated” in the
treatment of surgical wound infections.
Using an in vivo approach in a guinea pig
model, Stratford et al.  evaluated the effects
of lidocaine with and without epinephrine on
bacterial colonization of surgical wounds. Two
wounds on each animal were compared for
bacteria counts, one of which was infiltrated
with lidocaine (2%) and the other left untreated
prior to inoculation with S. aureus. The results
showed a ? 70% decrease in colony counts in
the wounds treated with plain lidocaine com-
pared with the controls. However, when epi-
nephrine was added, a 20-fold increase in
colony counts compared with controls was
found, suggesting that the hypoxia resulting
from vasoconstriction directly increases the risk
of surgical site infection. This study supports
the potential role of local anesthetics in the pro-
phylaxis of surgical site infection, provided
their vasodilating properties are not inhibited
by vasoconstrictors such as epinephrine.
The results of these investigations are pro-
vocative in that they reveal that these agents
have the potential to reduce to below an inva-
sive threshold the colony counts of bacteria and
fungi normally found in infected wounds.
These studies were performed with local anes-
thetic concentrations typically used in the clin-
ical setting (i.e., bupivacaine 0.125%, 0.25%,
and 0.5% and lidocaine 0.5%, 1.0%, and 2.0%).
As evidenced by numerous studies, local
anesthetics serve not only as agents for pain
control, but potentially as antimicrobial agents
as well. In that capacity, local anesthetics may
be considered an adjunct or alternative to tra-
ditional antimicrobial means in the clinical or
laboratory setting. As Parr et al. claimed ,
“wider application of the use of local anesthet-
ics should be mandated [in the treatment of
surgical site infection].” Additionally, caution
should be taken when administering local
anesthetics prior to diagnostic procedures in
which culture specimens are to be obtained, as
the antimicrobial activity of the local anesthetic
could lead to false-negative results or subopti-
mal culture yields. In such cases, it is recom-
mended by various authors that if use of a lo-
cal anesthetic cannot be avoided, the lowest
concentration possible of a mildly antimicro-
bial agent, such as cocaine or ropivacaine,
should be used in order to optimize culture
yields. The indirect effect of increased perfu-
sion resulting from peripheral vasodilation by
the local anesthetic, as well as the direct effect
of the local anesthetic’s ability to disrupt mi-
crobial cell membrane permeability and lead to
cell lysis, all appear to play a role in the an-
timicrobial capacity of local anesthetics.
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